The yarn feeding device known from EP 0 580 267 A1 comprises a pre-control device using the signals of a position sensor provided in the yarn feeding device in order to slowly drive the electric motor after switching off the electric motor by the speed control device until the winding element reaches a predetermined rotational position in relation to the housing. The control effort needed is considerable.
The yarn feeding device as known from EP 0 327 973 A (U.S. Pat. No. 4,936,356) is provided with a detector fixed to the housing which detector can be actuated by a transmitter rotating with the winding element in order to adjust the winding element with slow rotational speed into a predetermined position relative to the housing when the speed control device has to switch off the electric motor. The predetermined position of the winding element may be appropriate in order to facilitate threading of the yarn through the yarn feeding device.
U.S. Pat. No. 4,814,677 A generally discloses a field orientation control system of a permanent magnet motor operating by sinusoidal stator part actuation. The information on the momentary rotary position of the rotor is derived from measured stator voltages and stator currents. This is carried out without additional position sensors. The detected relative rotary positions of the rotor are used for the speed control and the torque control of the permanent magnet motor.
The so-called brushless DC motor (BLDC) known from EP 10 52 766 A2 (U.S. Pat. No. 6,356,048) is employed as the drive source for the winding element of a yarn feeding device. The motor is designed without sensors. A control system is provided for controlling the torque and/or the speed of the motor. The control system calculates the commutation switching points for the stator parts in six angled positions which are distant by a respective 60° without a position sensor. In this case the zero crossing points of the backwards acting electromotive force are determined which are induced in the stator windings by the rotation of the rotor magnets. In-between the six switching points, distributed about a full revolution, the position of the rotor remains unknown. The backwards acting electromotive force is effected according to a trapezoidal course. This motor drive control principle does not allow a sufficiently accurate position control and position observation of the winding element because only predetermined rotary positions of the rotor are detected.